sola hevi duty faq

Frequently Asked Questions For Sola Hevi-Duty Power Conditioners

Sola Hevi-Duty 3/19/2018

Although a constant voltage power conditioner (sometimes referred to as constant voltage transformer or voltage regulator) is a transformer-like device, its design and function are totally different. The function of a constant voltage power conditioner is to provide a voltage across its secondary terminals within a specified tolerance (usually ±5%) as long as the voltage impressed on the primary is within the specified bandwidth (usually +10% to -20%).

What are the differences among SolaHD power conditioners?

All three products use SolaHD’s ferroresonant technology. The primary design considerations for the CVS Series were voltage stabilization and magnetic isolation. This group provides ±1% output voltage regulation with an input voltage range of +10%/-20% with moderate (1000:1) normal (transverse) noise attenuation.

The MCR Series was designed to address both voltage regulation and magnetic isolation. This group offers ±3% output regulation with an input range of +10%/-20% but also offers magnetic isolation for excellent 1,000,000:1 common mode and 1000:1 normal (transverse) mode attenuation.

The Three Phase power conditioners utilize micro-processorbased tap switching technology to provide ±5% regulation in three phase installations. The CVS and MCR Series are single phase only.

Are there any special considerations needed when I select a constant voltage power conditioner?

Special consideration must be given to the type of load to be powered (inductive loads need to be sized to start-up currents), load power factor, ambient temperature and where the unit will be installed.

What exactly is Ferroresonance?

Ferroresonance is the principle behind SolaHD’s very popular CVS and MCR power conditioners. Ferroresonance is the property of a transformer design in which the transformer contains two separate magnetic paths with limited coupling between them. The output contains a parallel resonant tank circuit and draws power from the primary to replace power delivered to the load. Note that “resonance” in ferroresonance is similar to that in linear circuits with series or parallel inductors and capacitors, where the impedance peaks at a particular frequency. In a nonlinear circuit, such as SolaHD’s ferroresonant transformers, “resonance” is used to reduce changes in supply voltage to provide a more consistent voltage to the load.

A magnetic device is nonlinear. Its reluctance changes abruptly above a certain magnetic flux density. At this point, the magnetic device is defined as being in saturation. The design of the SolaHD transformer allows one magnetic path (the resonant path) to be in saturation, while the other is not (See Figure 1). As a result, further change in the primary voltage will not translate into changes in the saturated or secondary voltage and voltage regulation results.

Frequently Asked Questions For Sola Hevi-Duty Power Conditioners

Will harmonic currents affect ferroresonant power conditioners?

A SolaHD ferroresonant power conditioner will have essentially harmonic-free output because of the addition of a neutralizing coil. This coil neutralizes the harmonics in a manner best explained by first considering the device as a conventional transformer with the neutralizing coil disconnected. Though this coil is now open circuited, it has a voltage induced in it as a portion of the magnetic flux passes through the center leg of the core to the outer legs. Since some of the primary flux links this coil, fundamental voltage is present. The resultant voltage has a high odd-harmonic content due to the leakage flux from the output winding.

This leakage flux can return to the output winding by two paths. One bypasses the neutralizing coil. The other path links the neutralizing coil completely. By controlling the
reluctances of these magnetic paths, one can control the degree of secondary flux coupled to the neutralizing coil. The neutralizing coil is connected with its polarity additive to the secondary (or output coil) as shown in Figure 2. The output of the newly formed regulator has constant voltage with a waveshape almost completely free of harmonics.

The harmonics are still present in the output winding and also in the neutralizing coil. Since those harmonics present in the neutralizing coil are induced by the flux from the secondary winding, the harmonics in each coil are approximately 180° out of phase. This results in their cancellation. Proper control of turns ratio and magnetic path reluctance contribute to the generation of a sinusoidal output – even with a square wave input.

Frequently Asked Questions For Sola Hevi-Duty Power Conditioners

Are there different constant voltage power conditioner designs?

Yes, there are two basic design concepts. A tap switching design utilizes an electronic circuit along with a traditional transformer core and coil assembly to control the output voltage. As a result, the output voltage tends to be a stepped waveform rather than a smooth sinewave.

A ferroresonant design utilizes the electromagnetic induction principle exclusively to produce the desired  output voltage. Consequently, the output voltage waveform is a smooth sinewave. The ferroresonant design attenuates transient electrical noise, provides surge protection per ANSI/IEEE Standards and provides a harmonic-free output. These important benefits are not always available with other designs.